The invention relates to a plastic connecting piece (such as a sleeve or a T-connection saddle) intended for joining axially or transversely, and by heat-welding, two pipes, in particular in the gas industry, the invention relating more particularly to the improvement of the connection terminals of the electrically conducting resistance element with which said connecting device is equipped.
Such a device, which includes, for the heat-welded joining of two polyethylene pipes, an electrical heating resistance element consisting of a coiled electrically conducting wire embedded in the thickness of the piece in the vicinity of its internal welding surface, is already known from publications EP-A-0,149,410 or U.S. Pat. No. 4,684,417.
The welding operation is then carried out by placing opposite each other the pieces to be welded and by connecting the coiled electrical wire to an electrical source (such as a rectified source of alternating current) which, by the Joule effect, will heat up the resistance element and cause the softening until melting of the plastic surrounding the pieces, ensuring welding under pressure.
For the electrical connection of the resistance element, its two wire ends are usually each welded to a connection terminal each often emerging into a well or a cavity, so as to be able to constitute two pins which will be able to be plugged in, inside the said wells, to removable complementary sockets.
Still within the same field, other types of resistance elements can be used.
Thus, publication FR-A-2,654,978 provides the use of a single-wire net or of a grid which can be produced from a stretched metal plate.
However, the external electrical connection of this net or of this grid remains the same as the solution mentioned hereinabove. In the first case (single-wire net), the two ends of the wire are drawn out in order to be welded to the aforementioned pins. In the second case (stretched grid), it is advised to use two conducting plates fixed at two opposite ends of the grid, and two conducting joint cables welded on one side to the said plates and on the other side to the two aforementioned pins.
However, problems of reliability of the welded joints may then occur. There is also the risk that the fusion zone of the plastic body can end up damaging these joints, at the moment of the welding.
Furthermore, especially in the case of the use of a monofilar net, all this implies lengthy and tricky implementation operations.
Another solution is provided in Application EP-A-0,278,553. In this application, the connection terminals are applied to a connection piece in which a resistance element in the form of a coiled wire is embedded. These terminals each consist of two complementary pieces which are fitted into each other after having been inserted into the cavities provided for this purpose in the connecting piece. The two parts of the one same terminal, which are subjected to two opposed direction forces, are thus suitable for gripping a thin thickness of plastic where the resistance element passes and, once "clipped together", then establish an electrical contact with this resistance element. However, the use of such terminals necessitates producing tapped holes in the piece in order to insert therein the two complementary components of the terminals. On the other hand, the fitting of these components one into the other could lead (if the fitting forces are not very precisely applied), to a detrimental deformation of the connecting piece.